Fin-based photodetector structure

ABSTRACT

A photodetector disclosed herein includes an N-doped waveguide structure defined in a semiconductor material, wherein the N-doped waveguide structure comprises a plurality of first fins. Each adjacent pair of the plurality of first fins is separated by a trench formed in the semiconductor material. The photodetector also includes a detector structure positioned on the N-doped waveguide structure, wherein a portion of the detector structure is positioned laterally between the plurality of first fins. The detector structure comprises a single crystal semiconductor material. The photodetector also includes a first diffusion region that extends from the bottom surface of the trench into the semiconductor material, wherein the first diffusion region comprises atoms of the single crystal semiconductor material of the detector structure.

BACKGROUND Field of the Invention

The present disclosure generally relates to various novel embodiments of a fin-based photodetector structure and various methods of making such a structure.

Description of the Related Art

A need for greater bandwidth in fiber optic network links is widely recognized. The volume of data transmissions has seen a dramatic increase in the last decade. This trend is expected to grow exponentially in the near future. As a result, there exists a need for deploying an infrastructure capable of handling this increased volume and for improvements in system performance. Fiber optics communications have gained prominence in telecommunications, instrumentation, cable TV, network, and data transmission and distribution. A fiber optics communication system or link includes a photodetector element. The function of the photodetector element in a fiber optics communication system is to convert optical power into electrical voltage or current. The most common photodetector used in fiber applications is the semiconductor photodetector. There are many other applications where a photodetector may be employed, e.g., radiation detection, smoke detection, flame detection and to switch on relays for street lighting, etc. When incident light from, for example, a laser or an optical fiber irradiates the photodetector, light photons in the incident light are absorbed by the photodetector. The absorption of the light photons results in the creation of electron-hole pairs in the depletion region of the photodetector.

There is a need to produce a novel photodetector that is efficient to manufacture and may produce benefits with respect to the optical system or link in which such photodetectors are employed. The present disclosure is generally directed to various novel embodiments of a fin-based photodetector structure and various methods of making such a structure.

SUMMARY

The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an exhaustive overview of the invention. It is not intended to identify key or critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is discussed later.

The present disclosure is directed to various novel embodiments of a fin-based photodetector structure and various methods of making such a structure. One illustrative photodetector disclosed herein includes an N-doped waveguide structure defined in a semiconductor material, wherein the N-doped waveguide structure comprises a plurality of first fins. Each adjacent pair of the plurality of first fins is separated by a trench formed in the semiconductor material. The photodetector also includes a detector structure positioned on the N-doped waveguide structure, wherein a portion of the detector structure is positioned laterally between the plurality of first fins and wherein the detector structure comprises a single crystal semiconductor material. In this example, the photodetector also includes a first diffusion region that extends from the bottom surface of the trench into the semiconductor material, wherein the first diffusion region comprises atoms of the single crystal semiconductor material of the detector structure. The photodetector also includes at least one N-doped contact region positioned in the semiconductor material and a P-doped contact region positioned in the detector structure.

One illustrative method disclosed herein includes forming a plurality of first fins in an N-doped semiconductor material so as to define an N-doped waveguide structure, depositing a layer of amorphous semiconductor material on the N-doped waveguide structure, wherein portions of the layer of amorphous semiconductor material are positioned laterally between the plurality of first fins, and patterning the layer of amorphous semiconductor material to form a detector structure. In this example, the method also includes forming a layer of insulating material above the detector structure and performing a thermal melt growth process to convert substantially all of the layer of amorphous semiconductor material into a layer of single crystal semiconductor material.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements, and in which:

FIGS. 1-18 depict various novel embodiments of a fin-based photodetector structure and various methods of making such a structure. The drawings are not to scale.

While the subject matter disclosed herein is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION

Various illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

The present subject matter will now be described with reference to the attached figures. Various structures, systems and devices are schematically depicted in the drawings for purposes of explanation only and so as to not obscure the present disclosure with details that are well known to those skilled in the art. Nevertheless, the attached drawings are included to describe and explain illustrative examples of the present disclosure. The words and phrases used herein should be understood and interpreted to have a meaning consistent with the understanding of those words and phrases by those skilled in the relevant art. No special definition of a term or phrase, i.e., a definition that is different from the ordinary and customary meaning as understood by those skilled in the art, is intended to be implied by consistent usage of the term or phrase herein. To the extent that a term or phrase is intended to have a special meaning, i.e., a meaning other than that understood by skilled artisans, such a special definition will be expressly set forth in the specification in a definitional manner that directly and unequivocally provides the special definition for the term or phrase. As will be readily apparent to those skilled in the art upon a complete reading of the present application, the presently disclosed method may be applicable to a variety of products, including, but not limited to, logic products, memory products, etc. With reference to the attached figures, various illustrative embodiments of the methods and devices disclosed herein will now be described in more detail. The various components, structures and layers of material depicted herein may be formed using a variety of different materials and by performing a variety of known process operations, e.g., chemical vapor deposition (CVD), atomic layer deposition (ALD), a thermal growth process, spin-coating techniques, masking, etching, etc. The thicknesses of these various layers of material may also vary depending upon the particular application.

FIGS. 1-18 depict various novel embodiments of a fin-based photodetector structure 100 and various methods of making such a structure. FIG. 1 is a simplistic plan view of the photodetector 100 at an intermediate stage of fabrication. As depicted therein, the photodetector 100 comprises a plurality of fins 111 that were formed in a semiconductor substrate by etching a plurality of fin-formation trenches 110 into the substrate. Also depicted in FIG. 1 is an isolation structure 107 that is formed to electrically isolate the photodetector 100. The location where various cross-sectional views (view X-X) depicted herein is also shown in FIG. 1.

With reference to FIG. 2, in the examples depicted herein, the photodetector structure 100 will be formed above a semiconductor substrate 101. The substrate 101 may have a variety of configurations, such as a semiconductor-on-insulator (SOI) shown in FIG. 2. Such an SOI substrate 101 includes a base semiconductor layer 101A, a buried insulation layer 101B positioned on the base semiconductor layer 101A and an active semiconductor layer 101C positioned above the buried insulation layer 101B, wherein the photodetector structure 100 will be formed in and above the active semiconductor layer 101C. In one illustrative embodiment, the active semiconductor layer 101C may be an N+ doped material having a dopant concentration that falls within the range of about 1E18-1E20 ions/cm³. The location of the peak concentration of dopant atoms in the N+ doped active semiconductor layer 101C may also vary depending upon the particular application. The N+ doped active semiconductor layer 101C may be doped with any species of N-type dopant, e.g., arsenic, phosphorus, etc. In other applications, the substrate 101 may be made of silicon or it may be made of semiconductor materials other than silicon. Thus, the terms “substrate” or “semiconductor substrate” should be understood to cover all semiconductor materials and all forms of such materials.

FIG. 3 depicts the photodetector 100 after a trench 103 was formed in the active semiconductor layer 101C by performing known masking and etching techniques. The depth of the trench 103 may vary depending upon the particular application. As depicted in this illustrative embodiment, the trench 103 does not extend through the entire vertical thickness of the active semiconductor layer 101C.

FIG. 4 depicts the photodetector 100 after a layer of insulating material 105 was blanket-deposited across the substrate 101. The layer of insulating material 105 may be comprised of a variety of different materials, e.g., silicon dioxide.

FIG. 5 depicts the photodetector 100 after a planarization process, e.g., a chemical mechanical planarization (CMP) process, was performed to remove portions of the layer of insulating material 105 and to planarize its upper surface 105R. After the planarization process was completed, a relatively thin layer of the insulating material 105 (e.g. 5-50 nm) remains positioned above the upper surface 101S of the active semiconductor layer 101C. This process operation also results in the formation of the isolation structure 107.

FIG. 6 depicts the photodetector 100 after a patterned etch mask (not shown) was formed above the layer of insulating material 105 and after an etching process was performed to pattern the layer of insulating material 105. Thereafter, the patterned etch mask was removed.

FIG. 7 depicts the photodetector 100 after one or more etching processes were performed so as to define a plurality of fin-formation trenches 110 in the active semiconductor layer 101C. This etching process results in the formation of a plurality of fins 111 defined in the active semiconductor layer 101C. In the illustrative example where the active semiconductor layer 101C comprises silicon, these operations result in the formation of a silicon waveguide structure 104 that comprises the four illustrative upward extending fins 111. Of course, the photodetector 100 may comprise any number of fins 111 and may be comprised of a variety of different materials, e.g., a silicon-containing material, substantially pure silicon, silicon-germanium, etc. The depth and width of the trenches 110 may vary depending upon the particular application.

With continued reference to FIG. 7, the height and cross-sectional configuration of the fins 111 may also vary depending upon the particular application. In the examples depicted herein, the fins 111 will be depicted as have a simplistic rectangular cross-sectional configuration having a substantially uniform thickness throughout the height of the fins 111. In a real-world device, the fins 111 may have a tapered cross-sectional configuration wherein the width 111X of the upper surface 111S of the fin 111 (i.e., the fin top critical dimension) in the direction 106 is less than the width 111Y of the bottom of the fin 111 (i.e., the fin bottom critical dimension). In one illustrative embodiment, based upon current-day technology, the width 111X may be about 5-30 nm. Additionally, with reference to FIG. 1, the axial length 111Z of the fins 111 may also vary depending upon the particular application, e.g., 0.1-20 μm. Thus, the size and configuration of the fin-formation trenches 110 and the fins 111, and the manner in which they are made, should not be considered a limitation of the presently disclosed subject matter. Moreover, in the example depicted herein, the layer of insulating material 105 was patterned and used as a patterned etch mask to form the trenches 110 and the fins 111. In other process flows, a patterned etch mask (not shown) may be formed above the un-patterned layer of insulating material 105. Thereafter, one or more etching processes may be performed through the patterned etch mask to etch both the layer of insulating material 105 and to form the trenches 110.

FIG. 8 depicts the photodetector 100 after a conformal deposition process was performed to form a conformal layer of spacer material 130 above the substrate 101. The conformal layer of spacer material 130 may be comprised of a variety of different materials, e.g., silicon nitride, and it may be formed to any desired thickness, e.g., 1-6 nm.

FIG. 9 depicts the photodetector 100 after an anisotropic etching process was performed to remove substantially horizontally oriented portions of the conformal layer of spacer material 130. This process operation results in the formation of a sidewall spacer 130A on the sidewalls of the fins 111. Note that the bottom of the trenches 110 is exposed after the formation of the sidewall spacers 130A.

FIG. 10 depicts the photodetector 100 after a layer of amorphous material 132 was blanket-deposited across the substrate 101. The layer of amorphous material 132 may be comprised of a variety of different materials, e.g., a germanium-containing material, substantially pure germanium, silicon-germanium etc. Note that the layer of amorphous material 132 overfills the trenches 110 and its upper surface 132Y may be planarized if desired. In one illustrative embodiment, the layer of amorphous material 132 may be substantially free of any dopant material at this point in the process flow. In other embodiments, the layer of amorphous material 132 may comprise a P-type dopant material, and the dopant material may be added by way of an ion implantation process after the layer of amorphous material 132 is initially deposited or the dopant material may be added to the layer of amorphous material 132 as it is being formed, i.e., in situ doping. However, any dopant material present in the layer of amorphous material 132 at this point in the process flow may simply migrate in a more or less uncontrolled fashion during a thermal melt-growth process that is performed to convert the layer of amorphous material 132 to a crystalline structure, as described more fully below.

FIG. 11 depicts the photodetector 100 after a patterned etch mask (not shown) was formed above the layer of amorphous material 132 and after an etching process was performed to pattern the layer of amorphous material 132. Thereafter, the patterned etch mask was removed.

FIG. 12 depicts the photodetector 100 after a layer of insulating material 134 was blanket-deposited across the substrate 101 and above the layer of amorphous material 132. The layer of insulating material 134 may be comprised of a variety of different materials, e.g., silicon nitride.

FIG. 13 depicts the photodetector 100 after a known thermal melt-growth process 136 was performed to convert substantially all of the layer of amorphous material 132 to a single crystal crystalline structure 132C. In one illustrative embodiment, the thermal melt-growth process 136 may be performed at a temperature that falls within the range of about 800-1100° C. for a duration of about 10-120 minutes. In the case where the layer of amorphous material 132 comprises germanium, the crystalline structure 132C may be crystalline germanium. As will be appreciated by those skilled in the art after a complete reading of the present application, the crystalline structure 132C will function as the detector region or portion of the photodetector structure 100, and henceforth will be referred to as the detector structure 132C. Also note that, during the thermal melt-growth process 136, atoms from the layer of amorphous material 132, e.g., germanium atoms, may diffuse into the active semiconductor layer 101C at the bottom of the trenches 110, as reflected by the lower diffusion regions 132U. That is, the lower diffusion regions 132U comprise a composite crystalline material comprised of crystallized amorphous semiconductor material, e.g., crystallized germanium, and crystalline semiconductor material of the active semiconductor layer 101C, e.g., crystalline silicon.

Similarly, with continued reference to FIG. 13, during the thermal melt-growth process 136, atoms from the material of the active semiconductor layer 101C at the bottom of the trenches 110, e.g., silicon atoms, may also diffuse upward into the downward-extending fin-type structures 132X of the detector structure 132C that are positioned within the trenches 110, as reflected by the lower diffusion regions 133U (which are shown with a different shading relative to the lower diffusion regions 132U for purposes of explanation). That is, the lower diffusion regions 133U comprise a composite crystalline material comprised of crystallized amorphous semiconductor material, e.g., crystallized germanium, and crystalline semiconductor material of the active semiconductor layer 101C, e.g., crystalline silicon.

In one illustrative embodiment, the detector structure 132C may be substantially free of dopant material, e.g., an intrinsic semiconductor material, or it may be doped with a P-type dopant and become a P+ doped detector structure 132C. In the case where the detector structure 132C is a P+ doped detector structure 132C, the maximum concentration of dopant atoms in the P+ doped detector structure 132C may vary depending upon the particular application, e.g., 1E18-1E20 ions/cm³. The location of the peak concentration of dopant atoms within the vertical thickness of the P+ doped detector structure 132C may also vary depending upon the particular application. The P+ doped detector structure 132C may be doped with any species of P-type dopant, e.g., boron, boron difluoride, etc. Additionally, in some embodiments, only a portion of the vertical thickness of the P+ doped detector structure 132C may be doped with the P-type dopant. For example, below a depth (or thickness) of about 150-220 nm, the P+ doped detector structure 132C may be a substantially un-doped region (i.e., an intrinsic region), while the remaining portion of the vertical thickness of the P+ doped detector structure 132C is doped with the appropriate P-type dopant.

In the depicted example in FIG. 13, the detector structure 132C is a unitary structure that comprises a body portion 132D (positioned above the upper surface 111S of the fins 111), a plurality of downward-extending fin-type structures 132X that are positioned within the trenches 110 and interleaved with the upward extending fins 111 of the waveguide structure 104 (defined in the active semiconductor layer 101C), even though downward-extending fin-type structures 132X are separated from the fins 111 by the sidewall spacers 130A. The vertical thickness 132A of the body portion 132D may vary depending upon the particular application, e.g., 10-500 nm.

In the example shown in FIG. 13, the layer of amorphous material 132 (see FIG. 11) was patterned such that the resulting detector structure 132C comprises a unitary upper body portion 132D above the upper surface 111S of the fins 111. However, with reference to FIG. 14, in other applications, the layer of amorphous material 132 may be patterned in such a manner that the final detector structure 132C comprises a plurality of individual lines 132E of the material, as shown in FIG. 14. In the example shown in FIG. 14, a first portion of each of the elements 132E is positioned in the trenches 110 laterally between adjacent fins 111 while a second portion of each of the individual elements 132E is positioned above a level that corresponds to the upper surface 111S of the fins 111. For ease of presentation, the remaining depictions of the photodetector structure 100 will be based upon the illustrative embodiment shown in FIG. 13 where the detector structure 132C has a unitary structure comprising a body portion 132D and a plurality of downward-extending fins 132X.

FIG. 15 depicts the photodetector structure 100 shown in FIG. 13 after several process operations were performed. First, a patterned implant mask 138 was formed above the detector structure 132C. The patterned implant mask 138 may be comprised of a variety of different materials, e.g., photoresist, OPL, and it may be formed by performing traditional manufacturing techniques. Thereafter, at least one ion implantation process 140 may be performed to form a P+ doped region 142 in the detector structure 132C. The maximum concentration of dopant atoms in the P+ doped contact region 142 may vary depending upon the particular application, e.g., 1E18-1E20 ions/cm³. The vertical depth of the P+ doped contact region 142 and the location of the peak concentration of dopant atoms in the P+ doped contact region 142 within the vertical thickness of the detector structure 132C may also vary depending upon the particular application. The P+ doped region 142 may be doped with any species of P-type dopant, e.g., boron, boron difluoride, etc.

FIG. 16 depicts the photodetector structure 100 after another ion implantation process 144 was performed to form a P++ doped contact region 146 in the detector structure 132C. The maximum concentration of dopant atoms in the P++ doped contact region 146 may vary depending upon the particular application, e.g., 1E20-1E22 ions/cm³. The vertical depth of the P++ doped contact region 146 and the location of the peak concentration of dopant atoms in the P++ doped contact region 146 within the vertical thickness of the detector structure 132C may also vary depending upon the particular application. The P++ doped contact region 146 may be doped with any species of P-type dopant, e.g., boron, boron difluoride, etc.

FIG. 17 depicts the photodetector structure 100 after several process operations were performed. First, the patterned implant mask 138 was removed. Thereafter, another patterned implant mask 148 was formed above the substrate. The patterned implant mask 148 may be comprised of a variety of different materials, e.g., photoresist, OPL, and it may be formed by performing traditional manufacturing techniques. Thereafter, at least one ion implantation process 150 may be performed to form N++ doped contact regions 152 in the active semiconductor layer 101C. The maximum concentration of dopant atoms in the N++ doped contact regions 152 may vary depending upon the particular application, e.g., 1E20-1E22 ions/cm³. The vertical depth of the N++ doped contact regions 152 and the location of the peak concentration of dopant atoms in N++ doped contact regions 152 may also vary depending upon the particular application. The N++ doped contact regions 152 may be doped with any species of N-type dopant, e.g., arsenic, phosphorus, etc.

FIG. 18 depicts the photodetector structure 100 after several process operations were performed. First, the patterned implant mask 148 was removed. Thereafter, in one illustrative process flow, the layer of insulating material 134 may be removed. At that point, simplistically depicted one or more layers of insulating material 135 were formed above the photodetector structure 100. In a real-world device, the one or more layers of insulating material 135 may comprise multiple layers of material and the layers of material may be made of different materials. For example, the one or more layers of insulating material 135 may comprise one of more layers of silicon dioxide with a layer of silicon nitride (which functions as an etch stop layer) positioned between the layers of silicon dioxide. The structure, composition and techniques used to form such layer(s) of insulating material are well known to those skilled in the art. Thereafter, illustrative conductive contact structures 156 were formed to conductively contact the N++ doped contact regions 152 and an illustrative contact structure 154 was formed so as to conductively contact the P++ doped contact region 146. The structure, composition and techniques used to form such conductive contact structures 154, 156 are well known to those skilled in the art.

As will be appreciated by those skilled in the art after a complete reading of the present application, the novel photodetector 100 may be fabricated with a lower defect density as compared to at least some other photodetectors and may be more efficient while working in the sub-wavelength regime.

The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. For example, the process steps set forth above may be performed in a different order. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Note that the use of terms, such as “first,” “second,” “third” or “fourth” to describe various processes or structures in this specification and in the attached claims is only used as a shorthand reference to such steps/structures and does not necessarily imply that such steps/structures are performed/formed in that ordered sequence. Of course, depending upon the exact claim language, an ordered sequence of such processes may or may not be required. Accordingly, the protection sought herein is as set forth in the claims below. 

1. A photodetector, comprising: an N-doped waveguide structure defined in a semiconductor material, the N-doped waveguide structure comprising a plurality of first fins, wherein each adjacent pair of the plurality of first fins is separated by a trench formed in the semiconductor material, the trench comprising a bottom surface; a detector structure positioned on the N-doped waveguide structure, wherein a portion of the detector structure is positioned laterally between the plurality of first fins, wherein the detector structure comprises a single crystal semiconductor material; a first diffusion region that extends from the bottom surface of the trench into the semiconductor material, wherein the first diffusion region comprises atoms of the single crystal semiconductor material of the detector structure; at least one N-doped contact region positioned in the semiconductor material; and a P-doped contact region positioned in the detector structure.
 2. The photodetector of claim 1, wherein the first diffusion region further comprises atoms of the semiconductor material.
 3. The photodetector of claim 1, wherein the N-doped waveguide structure has a dopant concentration of an N-type dopant that falls within a range of 1E18-1E20 ions/cm³ and the detector structure is doped with a P-type dopant and has a dopant concentration of a P-type dopant that falls within a range of 1E18-1E20 ions/cm³.
 4. The photodetector of claim 1, wherein at least a portion of a vertical thickness of the detector structure is substantially free of a dopant material.
 5. The photodetector of claim 1, further comprising a sidewall spacer positioned on each of the plurality of first fins, wherein the portion of the detector structure is laterally separated from the plurality of first fins by at least the sidewall spacer positioned on each of the plurality of first fins.
 6. The photodetector of claim 1, wherein the detector structure is a unitary structure comprising a body and a plurality of second fins extending from the body, wherein the second fins are interleaved with the first fins.
 7. The photodetector of claim 1, wherein the detector structure comprises a plurality of individual elements, wherein at least one of the plurality of individual elements is positioned laterally between the plurality of first fins.
 8. The photodetector of claim 1, wherein the detector structure comprises one of a germanium-containing material, substantially pure germanium or silicon-germanium and wherein the N-doped waveguide structure comprises one of a silicon-containing material, substantially pure silicon or silicon germanium.
 9. The photodetector of claim 1, further comprising a second diffusion region that extends from the bottom surface of the trench into the portion of the detector structure that is positioned laterally between the plurality of first fins, wherein the second diffusion region comprises atoms of the semiconductor material.
 10. The photodetector of claim 2, wherein the second diffusion region further comprises atoms of the single crystal semiconductor material of the detector structure.
 11. A photodetector, comprising: an N-doped waveguide structure defined in a semiconductor material comprising silicon, the N-doped waveguide structure comprising a plurality of first fins, wherein each adjacent pair of the plurality of first fins is separated by a trench formed in the semiconductor material, the trench comprising a bottom surface; a detector structure positioned on the N-doped waveguide structure, wherein a portion of the detector structure is positioned laterally between the plurality of first fins, wherein the detector structure comprises single crystal germanium; a first diffusion region that extends from the bottom surface of the trench into the semiconductor material, wherein the first diffusion region comprises germanium atoms and silicon atoms; at least one N-doped contact region positioned in the semiconductor material; and a P-doped contact region positioned in the detector structure.
 12. The photodetector of claim 11, wherein the semiconductor material is an active semiconductor layer of a semiconductor-on-insulator (SOI) structure and wherein the semiconductor material comprises one of a silicon-containing material, substantially pure silicon or silicon germanium.
 13. The photodetector of claim 11, wherein at least a portion of a vertical thickness of the detector structure is substantially free of a dopant material.
 14. The photodetector of claim 11, further comprising a sidewall spacer positioned on each of the plurality of first fins, wherein the portion of the detector structure is laterally separated from the plurality of first fins by at least the sidewall spacer positioned on each of the plurality of first fins.
 15. The photodetector of claim 11, wherein the detector structure is a unitary structure comprising a body and a plurality of second fins extending from the body, wherein the second fins are interleaved with the first fins.
 16. The photodetector of claim 11, wherein the detector structure comprises a plurality of individual elements, wherein at least one of the plurality of individual elements is positioned laterally between the plurality of first fins.
 17. The photodetector of claim 11, further comprising a second diffusion region that extends from the bottom surface of the trench into the portion of the detector structure that is positioned laterally between the plurality of first fins, wherein the second diffusion region comprises germanium atoms and silicon atoms.
 18. A method, comprising: forming a plurality of first fins in an N-doped semiconductor material so as to define an N-doped waveguide structure; depositing a layer of amorphous semiconductor material on the N-doped waveguide structure, wherein portions of the layer of amorphous semiconductor material are positioned laterally between the plurality of first fins; patterning the layer of amorphous semiconductor material to form a detector structure; forming a layer of insulating material above the detector structure; with the layer of insulating material in position, performing a thermal melt growth process to convert substantially all of the layer of amorphous semiconductor material into a layer of single crystal semiconductor material; forming at least one N-doped contact region in the N-doped active semiconductor material; and forming a P-doped contact region in the detector structure.
 19. The method of claim 18, wherein the layer of amorphous semiconductor material comprises amorphous germanium and wherein the layer of single crystal semiconductor material comprises single crystal germanium.
 20. The method of claim 18, wherein performing the thermal melt growth process comprises performing the thermal melt growth process so as to form a first diffusion region that extends from the bottom surface of the trench into the semiconductor material, wherein the first diffusion region comprise atoms of the single crystal semiconductor material of the detector structure. 